Method of making encapsulated capacitor



y 966 G. R. PEARCE ETAL 3,261,902

METHOD OF MAKING ENGAPSULATED CAPACITOR Filed Sept 8, 1964 2Sheets-Sheet 1 FIG. 5

INVENTORS.

GODFREY R. PEARCE LAWRENCE R. SPARROW JERRY BRA/MAN F1626 ayfig ATTORNEYJuly 19, 1966 e. R. PEARCE ETAL METHOD OF MAKING ENGAPSULATED CAPACITOR28heets-Sheet 2 Filed Sept. 8, 1964 INVENTORS. DFREY R. PEARCE IAWRENCE, R. SPARROW JERRY BRA/MAN ATTORNEY FIG. 10

United States Patent 3,261,902 METHOD OF MAKING ENCAPSULATED CAPACITORGodfrey R. Pearce, Lawrence, and Lawrence R. Sparrow and Jerry Braiman,Indianapolis, Ind., assignors to P. R. Mallory & Co., Inc.,Indianapolis, Ind., a corporation of Delaware Filed Sept. 8, 1964, Ser.No. 394,838

' 7 Claims. (Cl. 264--272) The present invention relates to electrolyticdevices and more particularly relates to means and methods for providinga seal for electrolytic capacitors by encapsulation.

Prior experience in the capacitor art has clearly established the needfor providing eflicient protective sealing means for capacitor units.The sealing means must be moisture resistant, resistant to chemicalattack, resistant to vapors, resistant to heat distortion, mechanicallyrigid, capable of containing electrolyte and capable of preserving theelectrolyte and capable of preserving the electrical properties of thecapacitor units.

The continual advancement of plastics technology has brought forth theuse of many materials for capacitor encapsulation. Furthermore, thedevelopment of new and improved molding techniques has afforded greatflexibility in encapsulation methods. However, it is not known in theart to mold directly to the wet capacitor body. There are known methodswherein the wound capacitor body is placed in a premolded sleeve, a plugor stopper is inserted into the hollow ends of said sleeve to provide asealing means, a mass of plastic is injected over the plug to increasethe sealing eifect. This provides a presealed capacitor which ispackaged in plastic as described in. the Miquielis patent, US. PatentNo. 2,970,182, issued J an. 31, 1961. The intermediate step in themultistage sealing process of inserting a stopper or plug to each end ofthe capacitor'body was thought necessary to prevent physical disturbanceof the capacitor body from the elevated molding pressures andtemperatures. It was previously thought impossible to mold directly to awet unit.

A long-standing need has existed, therefore, for means and methodswhereby an encapsulated capacitor assembly having superior physical,mechanical and electrical properties can be economically produced with ahigh degree of reliability. The present invention meets this need andhas hereupon contributed an extraordinary advancement in the capacitorart.

It is, therefore, an object of the present invention to provide a novelmethod for providing an extremely economical encapsulated capacitorwhich overcomes the disadvantages of prior art.

It is an object of the present invention to provide a method for makingan encapsulated capacitor with a homogeneous casing having excellentmechanical rigidity, high resistance to heat distortion, outstanding lowtemperature physical characteristics, low thermal coeificient ofexpansion, and extremely low moisture absorption.

Another object of the present invention is to provide a method forencapsulating a capacitor body which is impregnated with a suitableliquid non-polymerizable electrolyte.

It is an object of the present invention to disclose a novel two-stageencapsulation technique which permits molding end seals around a wetunit.

It is further an object of the present invention to guarantee a safeminimum wall thickness of the capacitor casing by means of a two-stagemolding process wherein a pre-formed housing section is employed as thefirststage element.

Still another object of the present invention is to utilize a novelmethod for making an efiiciently pre-impregnated 3,261,902 Patented July19, 1966 capacitor body housed in a preformed case and to mold directlyto the wet capacitor body.

The present invention, in another of its aspects, relates to novelfeatures of the instrumentalities described herein for teaching theprincipal object of the invention and to the novel principles employedin the instrumentalities, whether or not these features and principlesmay be used in the said object and/ or in the said field.

Other objects of the invention and the nature thereof will becomeapparent from the following description taken in conjunction with theaccompanying figures of the drawing and wherein like referencecharacters describe elements of similar function therein and wherein thescope of the invention is determined rather from the dependent claims.

For illustrative purposes, the invention will be described in connectionwith the accompanying drawings in which:

FIGURE 1 is a perspective view of a typical pre-impregnated, convolutelywound capacitor body with axial terminal wires attached, capable ofbeing provided with a plastic casing according to the present invention.

FIGURE 2 is a longitudinal sectional view of a preformed plasticcylindrical sleeve.

FIGURE 3 is a sectional view of the capacitor body positioned in thepre-formed sleeve.

FIGURE 4 is an end view of the pre-formed sleeve.

FIGURE 5 is a sectional view of the capacitor after molding.

FIGURE 6 is a view in perspective of the molded, axial lead capacitor.

FIGURE 7 is a perspective view of a typical pre-impregnated, convolutelywound capacitor body with single end leads attached, prior toencapsulation.

FIGURE 8 is a sectional view of a preformed sleeve for the single-endunit.

FIGURE 9 is a sectional view of the capacitor body positioned in thesleeve prior to molding.

FIGURE 10 is a sectional view of the molded, single end lead capacitor.

FIGURE 11 is a perspective view of the molded, singleended leadcapacitor.

Generally speaking, the present invention provides means or methods foreconomically encapsulating a wet capacitor body within a thermoplasticcasing through a two-stage molding process. The initial step of thetwostage process consists of molding a thermoplastic casing in ageometrical shape substantially equivalent to the contour of thepreimpregnated capacitor body to be encased. Depending upon theparticular geometry of the part to be encased, either one or two closuresurfaces are intentionally omitted from the preformed sleeve, therebypermitting rapid insertion of the capacitor body within the sleeve inpreparation for the final molding stage.

The capacitor is then positioned ina suitable mold cavity and athermoplastic compatible with the sleeve material is injected into theremaining closures, thereby producing a capacitor assembly with superiorphysical, mechanical and electrical properties.

Two representative embodiments of the present invention will bedescribed in detail herein as being illustrative of the special featuresof the invention. One embodiment comprises the encapsulation of an axiallead capacitor, and the second embodiment comprises the encapsulation ofa single ended capacitor.

Referring now to the drawings, the convolutely Wound capacitor body 10shown in FIGURE 1 is substantially cylindrical in shape, and is usuallynot more than a fraction of an inch in diameter and not more than twoinches in length, although not confined to said specifications. Theillustrative example shown herein is an aluminum foil sheet interwoundwith an absorbent material such a as paper, and impregnated with aliquid electrolyte such as a compounded mixture consisting principallyof ethylene glycol and boric acid, although not limited to such. A metaltab 11 is provided at each end of the cylindrical body for attachment ofterminal wires 12 and 13. Terminal wires 12 and 13 are welded to therespective capacitor tabs at junction 14.

FIGURE 2 is a sectional view of the preformed cylindrical thermoplasticsleeve 15, which constitutes the first step in the two-stage moldingprocess of the present invention. As sleeve 15 is individuallyfabricated, the physical dimensions thereof can be controlled asnecessary to insure adequate wall strength in the event that no additionof thermoplastic material occurs to the inside cylindrical wall duringthe final encapsulation process. Sleeve 15 may be formed as shown inFIGURE 2 or with a positioning shoulder 16 as shown in FIGURE 3.Shoulder 16 serves as a positioning means for capacitor 10.

FIGURE 3 shows capacitor 10 oriented inside sleeve 15 with leads 12 and13 projecting therefrom. Sleeve 16 serves as a positioning means toinsure adequate seal strength at both ends of the completed unit.

FIGURE 4 is an end view of sleeve 15 showing recessed shoulder 16 havingaperture 17 with lead 13 projecting therefrom.

FIGURE illustrates the completed encapsulated capacitor 18. As can beseen from the drawing, the injection of end seals produces a homogeneoushousing of thermoplastic material 19 having superior protectiveproperties. Mechanical closure around leads 12 and 13 is insured by atit formation 20. Owing to the shrinkage characteristics of thethermoplastics, an extension 0.040 inch to 0.200 inch long and 0.004inch to 0.040 inch thick per side about the wire insures a seal. It canbe further seen in FIGURE 5 that the injected plastic forms a sealbetween the wet capacitor body and capacitor tabs 11 and 11a andguarantees encapsulation of welds 14 and 14a thereby preventing contactbetween welds 14 and 14a and the electrolyte, which would result incorrosion of the weld.

The view in perspective of the encapsulated capacitor 18 shown in FIGURE6 reveals the smooth, compact and functional appearance of thecapacitor, with only terminal wires 12 and 13 and molded sealing tit 20projecting therefrom. It has been found that no special pluggingprovisions are necessary for insuring tightness of the end seal aroundterminal wires 12 and 13 as the end closure material effects a securebond thereto.

Referring to FIGURES 7 through 11 for an illustration of a secondembodiment of the present invention, encapsulation of a single-endedlead capacitor is contemplated. FIGURE 7 shows a convolutely woundpreimpregnated capacitor body 30 having anode tab 31 and cathode tab 32extending from a single end of capacitor 30. Tabs 31 and 32 have leads33 and 34 welded thereto at junctions 35 and 36. The preformedcylindrical sleeve having one open end is shown in FIGURE 8. Capacitor30 is positioned in sleeve 37 as shown in FIGURE 9 and an end seal of athermoplastic compatible with that of sleeve 37 is injected.

FIGURE 10 shows the encapsulated capacitor 38 after injection of an endseal. It can be seen that the injected plastic has formed a unitary bodywith the preformed sleeve 3-7 (FIGURE 9) and that the injected plasticforms .a seal between the wet capacitor body 30 and capacitor tabs 31and 32 and guarantees encapsulation of weld joints 35 and 36 therebypreventing electrolyte corrosion at joints 35 and 36. Molded sealing tit39 is utilized to ensure a good mechanical seal.

FIGURE 11 is a perspective view of the encapsulated capacitor 38 showingthe smooth, compact and functional appearance thereof, with onlyterminal wires 34 and 35 and end tit 39 projecting therefrom.

Successful encapsulation by the molding process of the present inventionhas been consistently repeated with a number of thermoplastic materialssuch as polypropylene, polyethylene, polyamide, polystyrene,polycarbonate, and polyurethane resins. However, polypropylene resinsare preferred for economic reasons and the physical properties obtained.

The present invention, therefore, discloses means for producing anefficient, economical and reliable molded capacitor, encapsulated with asuitable thermoplastic and having the following specific advantages:desirably low differential expansion between the encasement material andthe thermal wires; high heat distortion level so as to resist solderingheat; superior molding characteristics which provide completecoalescence between the molten mass being introduced and the preformedcasing, both of like material; extremely low moisture absorption; highimpact strength and rigidity; thermal self venting and gas permeability;and retention of good physical properties at temperatures as low as -55C.

The two-stage molding process of the present invention offers one verydistinct advantage, viz., the assurance that the wall thickness of thefinished capsule can never be less than the wall thickness of thepreformed sleeve, regardless of how badly misaligned the capacitor bodyhecomes during processing. A collateral advantage of this process is theoption of using any desired coloring in the second-stage molding processto identify polarity on axial lead capacitor units. Furthermore, totalencapsulation of the terminal connection prevents inadvertent contactbetween the elecrolyte and the connector parts, thus avoiding corrosioneffects thereupon. The main advantage of the present invention is themolding of end seals directly to a wet unit, which was heretoforethought impossible by those skilled in the art.

The encapsulated capacitor of the present invention, as hereinbeforedescribed, in merely illustrative and not exhaustive in scope. Sincemany widely different embodiments of the invention may be made withoutdeparting from the scope thereof, it is intended that all mattercontained in the above description and shown in the accompanying drawingshall be interposed as illustrative and not in a limiting sense. Havingthus described our invention,

We claim:

1. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of pre-forming an openend thermoplastic sleevesubstantially equivalent in shape to the contour of a capacitor body tobe encased, said capacitor body being impregnated with a suitable liquidnon-polymerizable electrolyte, placing said capacitor body inside saidpreformed sleeve so that only the terminal wires of said capacitor bodyproject therefrom, positioning said pre-formed sleeve and said capacitorbody within a suitable mold cavity having protuberances at points oflead egress introducing into said mold cavity a molten thermoplasticmaterial having fusion characteristics equivalent to those of saidpre-formed sleeve, introducing said molten material in such a physicalstate whereby complete coalescence with said pre-formed casing isachieved, and flowing said molten material into said protuberances andaround the leads to seal the same tightly therein, thereby producing aunitary capacitor capsule adhering to said terminal wires to form atight seal therewith.

2. method of encapsulating an electrolytic aluminum capacitor comprisingthe steps of pre-forming thermoplastic sleeve substantially equivalentin shape to the contour of a convolutely wound, axial lead capacitorbody to be encased, said capacitor body being impregnated with asuitable liquid non-polymerizable electrolyte, said sleeve having twoopen ends, one of said ends having a recessed shoulder means having anaperture for lead projection associated therewith for positioning saidcapacitor body within said sleeve to insure even end seals, placing saidimpregnated capacitor body inside said pre-formed sleeve so that onlysaid axial leads of said capacitor body project therefrom; positioningsaid pre-formed sleeve containing said capacitor body within a suitablemold cavity having protuberances at points of lead egress for forming atit formation about terminal wires attached to said axial leads;introducing into said mold cavity a molten thermoplastic material havingfusion characteristics equivalent to those of said pre-formed sleeve,and introducing said thermoplastic material in such a physical statewhereby the resulting molded end seals coalesce with said preformedsleeve and form said titformation about said terminal wires, therebyproducing a unitary capacitor capsule adhering to said terminal wires toform a tight seal therewith.

3. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of pre-forming a thermoplastic sleeve substantiallyequivalent in shape to the contour of a convolutely wound, single-endedlead capacitor body to be encased, said capacitor body being impregnatedwith a suitable liquid non-polymerizable electrolyte; said sleeve havingone open end, placing said impregnated capacitor body inside saidpre-formed sleeve so that only said leads of said capacitor body projecttherefrom; positioning said pre-formed sleeve containing said capacitorbody within a suitable mold cavity having protuberances at points oflead egress for forming a tit formation about terminal wires attached tosaid axial leads; introducing into said mold cavity a moltenthermoplastic material having fusion characteristics equivalent to thoseof said pre-formed sleeve; and introducing said thermoplastic materialin such a physical state whereby the resulting moldedend seals coalescewith said pro-formed sleeve and form said tit formation about saidterminal wires, thereby producing a unitary capacitor capsule adheringto said terminal wires to form a tight seal therewith.

4. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of pre-forming a polypropylene sleeve substantiallyequivalent in shape to the contour of a convolutely wound, axial leadcapacitor body to be encased, said capacitor body being impregnated witha suitable liquid non-polymerizable electrolyte; said sleeve having twoopen ends, one of said ends having a recessed shoulder means having anaperture for lead projection associated therewith for positioning saidcapacitor body within said sleeve to insure even end seals, placing saidimpregnated capacitor body within said preformed sleeve so that onlysaid axial leads of said capacitor body project therefrom; positioningsaid pre-formed sleeve containing said capacitor body within a suitablemold cavity having protuberances at points of lead egress for forming atit formation about terminal wires attached to said axial leads;introducing molten polypropylene into said mold cavity in such aphysical state whereby the resulting end seals coalesce with saidpre-formed sleeve and form said tit formation about said terminal wires,thereby producing a unitary capacitor capsule as adhering to saidterminal wires to form a tight seal therewith.

5. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of preforming a polyethylene sleeve substantiallyequivalent in shape to the contour of a convolutely wound, axial leadcapacitor body to be encased, said capacitor body being impregnated witha suitable liquid non-polymerizable electrolyte; placing saidimpregnated capacitor body inside said preformed sleeve so that onlysaid axial leads of said capacitor body project therefrom; positioningsaid sleeve containing said capacitor body within a suitable mold cavityhaving protuberances at points of lead egress for forming a titformation about terminal wires attached to said axial leads; introducingmolten polyethylene into said mold cavity in such a physical statewhereby the resulting molded end seals coalesce with said preformedsleeve and form said tit formation about said terminal wires, therebyproducing a unitary capacitor capsule adhering to said terminal wires toform a tight seal therewith.

6. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of preforming a polypropylene sleeve substantiallyequivalent in shape to the contour of a convolutely wound, single-endedlead capacitor body to be encased, said capacitor body being impregnatedwith a suitable liquid non-polymerizable electrolyte; said sleeve havingone open end; placing said impregnated capacitor body within saidpreformed sleeve so that only said axial leads of said capacitor bodyextend therefrom; positioning said preformed sleeve and said capacitorbody within a suitable mold cavity having protuberances at points oflead egress for forming a tit formation about terminal wires attached tosaid axial leads; introducing molten polypropylene into said mold cavityin such a physical state whereby the resulting molded end seals coalescewith said preformed sleeve and form said tit formation about saidterminal wires, thereby producing a unitary capacitor capsule adheringto said terminal wires to form a tight seal therewith.

7. A method of encapsulating an electrolytic aluminum capacitorcomprising the steps of preforming a polyethylene sleeve substantiallyequivalent in shape to the contour of a convolutely wound, single-endedlead capacitor body to be encased, said capacitor body being impregnatedwith a suitable liquid non-polymerizable electrolyte; said sleeve havingone open end; placing said impregnated capacitor body within saidpreformed sleeve so that only the terminal wires of said capacitor bodyproject therefrom; positioning said preformed sleeve containing saidcapacitor body within a suitable mold cavity having protuberances atpoints of lead egress for forming a tit formation about terminal wiresattached to said axial leads; introducing molten polyethylene into saidmold cavity in'such a physical state whereby the resulting molded endseals coalesce with said preformed sleeve and form said tit formationabout said terminal wires, thereby producing a unitary capacitor capsuleadhering to said terminal wires to form a tight seal therewith.

References Cited by the Examiner UNITED STATES PATENTS 2,101,896 12/1937Burlingame 317-260 2,107,132 2/1938 Smith 217260 2,552,999 5/1951Pannell et al. 264--272 2,611,930 9/1952 Hill et al. 264272 2,713,700 7/1955 Fisher 264272 X 2,949,640 8/1960 Collins et al. 264272 X 2,970,1821/1961 Miguelis 264--272 X FOREIGN PATENTS 66,972 6/ 1948 Denmark.1,272,045 8/1961 France. 1,272,046 8/ 1961 France.

N6225 VIII d/21c 4/1956 Germany.

ROBERT F. WHITE, Primary Examiner. JOHN F. BURNS, Examiner.

D. J. BADER, F. MARLOWE, L. S. SQUIRES,

Assistant Examiners.

1. A METHOD OF ENCAPSULATING AN ELECTROLYTIC ALUMINUM CAPACITORCOMPRISING THE STEPS OF PRE-FORMING AN OPENEND THERMOPLASTIC SLEEVESUBSTANTIALLY EQUIVALENT IN SHAPE TO THE CONTOUR OF A CAPACITOR BODY TOBE ENCASED, SAID CAPACITOR BODY BEING IMPREGNATED WITH A SUITABLE LIQUIDNON-POLYMERIZABLE ELECTROLYTE, PLACING SAID CAPACITOR BODY INSIDE SAIDPRE-FORMED SLEEVE SO THAT ONLY THE TERMINAL WIRES OF SAID CAPACITOR BODYPROJECT THEREFROM, POSITIONING SAID PRE-FORMED SLEEVE AND SAID CAPACITORBODY WITHIN A SUITABLE MOLD CAVITY HAVING PROTUBERANCES AT POINTS OFLEAD EGRESS INTRODUCING INTO SAID MOLD CAVITY A MOLTEN THERMOPLASTICMATERIAL HAVING FUSION CHARACTERISTIC EQUIVALENT TO THOSE OF SAIDPRE-FORMED SLEEVE, INTRODUCING SAID MOLTEN MATERIAL IN SUCH A PHYSICALSTATE WHEREBY COMPLETE COALESCENCE WITH SAID PRE-FORMED CASNG ISACHIEVED, AND FLOWING SAID MOLTEN MATERIAL INTO SAID PROTUBERANCES ANDAROUND THE LEADS TO SEAL THE SAME TIGHTLY THEREIN, THEREBY PRODUCING AUNITARY CAPACITOR CAPSULE ADHERING TO SAID TERMINAL WIRES TO FORM ATIGHT SEAL THEREWITH.